A major emphasis of this project is the determination of the amino acid sequence of pregnant mare serum gonadotropin. The sequence of alpha subunit has been determined. The beta subunit requires clarification of the sequence near the C-terminus, which we hope to achieve during the current year. Homology of this sequence to that of luteinizing hormone of several species and hCG is very high. Placement of disulfide bonds in the LH beta subunit has been studied and studies are in progress for LH alpha disulfide placements. Acid-labile points in the amino acid sequence of ovine LH alpha have been observed. This has led to an examination of subunit isolation procedures, the modification of which permit total recovery of activity upon subunit recombination. Further examination of luteinizing hormone for other types of structural lability is in progress.